The spine is formed of superposed vertebrae, normally aligned along a vertebral axis, from the lumbar vertebrae, through the thoracic vertebrae, and to the cervical vertebrae, each having a posterior wall from which projects a spinous process and two lateral edges from the walls from which project ribs and/or transverse processes and/or lamina, each having a pedicle. If the spine of a person has abnormal curvature, such as from scoliosis, the vertebrae are typically inclined relative to one another and relative to the vertebral axis.
In order to straighten the vertebral column as a remedy for this situation, the lateral edges of the vertebrae on the concave side can be moved away from one another and supported at distances from one another substantially equivalent to the distances between the lateral edges on the other side. Devices known in the art for holding the vertebrae relative to one another include rigid and dynamic stabilization using stiff or flexible rods that are held by rod-receiving elements, such as bone anchors, attached to the vertebrae, for example using screws, hooks, or flexible ligatures.
Assembly of the rods to the rod receiving elements can typically be carried out in the operating room intraoperatively, after the rod-receiving elements have been surgically anchored to an osseous structure of the patient. Once the rods have been positioned, they can be manipulated into a position to straighten the spinal column. In order to facilitate manipulation of the rods, various instruments can be used, such as persuaders and derotators.